如何使用GLUT在按键上绘制形状？

Question

我想按空格键时画一个圆柱体。

这是代码的摘录我现在所拥有的：

void draw_cylinder(GLfloat radius, 
    GLfloat height, 
    GLubyte R, 
    GLubyte G, 
    GLubyte B) 
{ 
    GLfloat x = 0.0; 
    GLfloat y = 0.0; 
    GLfloat angle = 0.0; 
    GLfloat angle_stepsize = 0.1; 

    /** Draw the tube */ 
    glColor3ub(R - 40, G - 40, B - 40); 
    glBegin(GL_QUAD_STRIP); 
    angle = 0.0; 
    while (angle < 2 * 3.141) { 
     x = radius * cos(angle); 
     y = radius * sin(angle); 
     glVertex3f(x, y, height); 
     glVertex3f(x, y, 0.0); 
     angle = angle + angle_stepsize; 
    } 
    glVertex3f(radius, 0.0, height); 
    glVertex3f(radius, 0.0, 0.0); 
    glEnd(); 

    /** Draw the circle on top of cylinder */ 
    glColor3ub(R, G, B); 
    glBegin(GL_POLYGON); 
    angle = 0.0; 
    while (angle < 2 * 3.141) { 
     x = radius * cos(angle); 
     y = radius * sin(angle); 
     glVertex3f(x, y, height); 
     angle = angle + angle_stepsize; 
    } 
    glVertex3f(radius, 0.0, height); 
    glEnd(); 
} 

void display() { 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glMatrixMode(GL_MODELVIEW); 
} 

void reshape(GLsizei width, GLsizei height) { 
    if (height == 0) height = 1; 
    GLfloat aspect = (GLfloat)width/(GLfloat)height; 

    glViewport(0, 0, width, height); 

    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity();    
    gluPerspective(35.0f, aspect, 0.1f, 100.0f); 
} 

void processKeys(unsigned char key, int x, int y) { 

    if (key == 32) { // space key 
     glLoadIdentity(); 
     glTranslatef(0.0, -0.4, -5.0); 
     glRotatef(-90, 0.4, 0.0, 0.0); 
     draw_cylinder(0.3, 1.0, 255, 160, 100); 
    } 
    glutPostRedisplay(); 
} 

int main(int argc, char** argv) { 
    glutInit(&argc, argv);   // Initialize GLUT 
    glutInitDisplayMode(GLUT_DOUBLE); // Enable double buffered mode 
    glutInitWindowSize(640, 480); // Set the window's initial width & height 
    glutInitWindowPosition(50, 50); // Position the window's initial top-left corner 

    glutCreateWindow(title);   // Create window with the given title 
    glutKeyboardFunc(processKeys); 
    glutDisplayFunc(display);  // Register callback handler for window re-paint event 
    glutReshapeFunc(reshape);  // Register callback handler for window re-size event 
    initGL();      // Our own OpenGL initialization 
    glutMainLoop();     // Enter the infinite event-processing loop 

    return 0; 
} 

然而，当我按下空格键，气缸不绘制。我不知道该怎么做。当我复制我在processKeys方法中的代码并将其粘贴到显示器方法中时，它工作正常。 我该怎么做？

Answer 1

如函数名称所示，使用display函数绘制对象。因此，为了实现你想要的，创建一个布尔变量（例如全局范围），并使用它来控制是否要绘制圆柱体。例如：

bool cylinder_draw = false; 

void display() { 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glMatrixMode(GL_MODELVIEW); 
    if (cylinder_draw) { 
     glLoadIdentity(); 
     glTranslatef(0.0, -0.4, -5.0); 
     glRotatef(-90, 0.4, 0.0, 0.0); 
     draw_cylinder(0.3, 1.0, 255, 160, 100); 
    } 
} 

void processKeys(unsigned char key, int x, int y) { 

    if (key == 32) { // space key 
     cylinder_draw = true; 
    } 
    glutPostRedisplay(); 
}